1. Field of the Invention
The present invention relates to memory devices and methods, specifically to memory devices and methods capable of storing more than two states.
2. Description of the Related Art
Currently one of the most popular memory technologies uses either a form of MOS (metal-oxide-semiconductor) or CMOS (complementary metal-oxide-semiconductor) processes. However, it is well known that this technology requires constant refreshing of each memory cell to maintain the logic signal strength due to the inherent leakage of capacitors. The constant refreshing of the memory cells is not a problem when there is an unlimited voltage source, but in many applications, like laptop computers and cell phones, there is a finite supply. To deal with this problem, rechargeable batteries have been used in all portable electrical devices.
The problem with using devices that have capacitive memory arrays is the inconvenience in keeping the batteries properly charged every few hours. Therefore, there is a need for a non-volatile memory device that does not need to be refreshed and is inexpensive and quick to make. Additionally, in a ferromagnetic memory array, it has generally been necessary to provide a wholly separate circuit to detect the polarity, and thus the binary value, of the remnant magnetic field of a ferromagnetic digital memory cell. For example, many current ferromagnetic memories use such techniques as “giant magneto resistance” and the Hall effect to sense the magnetic polarity of memory bits. These require circuitry in addition to that used for state change, and in some cases many extra steps to fabricate. The requirement of a separate sensing circuit adds considerably to the time and expense of fabrication. This additional circuitry also limits the density of the memory cells in an array, and effects the time required to read, or sense the magnetic polarity, or value.
In the digital memory arena, especially random access memory, fast, dense non-volatility is an advantage. Accordingly, it is desirable to have a non-volatile memory array wherein the remnant magnetic field is sensed with the same circuitry used to write, or effect the state change of, a ferromagnetic bit in such a memory cell.
Some improvements have been made in the field. Examples of references related to the present invention are described below, and the supported teachings of each reference are incorporated by reference herein:
U.S. Pat. No. 7,123,050 to Lienau and entitled Programmable array logic circuit employing non-volatile ferromagnetic memory cells describes a programmable array logic circuit whose temporary memory circuitry employs single bit non-volatile ferromagnetic memory cells. The ferromagnetic memory cells or bits store data even when there is no power provided to the circuitry, thus saving power during operation of the programmable logic circuitry, and ensuring that there is no loss of the data should there be a temporary power shut down. Additionally, the ferromagnetic cells provide for indefinite number of switching actions on the data without degradation to the capacity to store data therein. There is described an integrated circuit, comprising a programmable logic circuit array having product lines and input lines therein, and a storage register circuit. The storage register circuit has a ferromagnetic bit and sensor coupled to store a remnant control signal and an output transistor, coupled to be responsive to the remnant control signal on its gate, and coupled between an input and product line. Additionally, the integrated circuit may further include a logical AND array and a logical OR array.
U.S. Pat. No. 7,023,727 to Lienau and entitled Non-volatile ferromagnetic memory having sensor circuitry shared with its state change circuitry describes a ferromagnetic memory cell is disclosed having a base, oriented in a horizontal plane, a bit, made of a ferromagnetic material, and a sense/write line, positioned proximate the bit sufficient to detect the directed polarity of the bit when a first current is applied thereto, and to direct the polarity of the bit when a second larger current is applied thereto in a given direction. The bit has a height that is oriented perpendicular to the horizontal plane of the base, and a polarity that can be directed along the height.
U.S. Pat. No. 6,873,546 to Lienau and entitled Method and apparatus for reading data from a ferromagnetic memory cell describes a ferromagnetic memory cell is disclosed. The cell includes a bit, made of a ferromagnetic material, having a remnant polarity. The cell also includes a read drive line coupled to a first portion of the bit, to feed a current into the bit. A sense conductor is coupled to a second portion of the bit, to receive the current from the bit. The current conducted through the bit is responsive to the polarity of the bit. A method is also disclosed for determining the magnetic polarity of a ferromagnetic bit. In this method, a bit is provided that is made of ferromagnetic material and has a remnant polarity. An input current is fed into the bit through a read drive line coupled to a first portion of the bit. An output current is received from the bit through a sense conductor coupled to a second portion of the bit. The current conducted through the bit is responsive to the polarity of the bit. A variance between the input current and output current is then sensed, from which the magnetic polarity of the bit is determined.
U.S. Pat. No. 6,864,711 to Lienau and entitled Programmable array logic circuit whose product and input line junctions employ single bit non-volatile ferromagnetic cells describes a programmable array logic circuit whose temporary memory circuitry employs single bit non-volatile ferromagnetic memory cells. There is described an integrated circuit, comprising a programmable logic circuit array having product lines and input lines therein, and a storage register circuit. The storage register circuit has a ferromagnetic bit and sensor coupled to store a remnant control signal and an output transistor, coupled to be responsive to the remnant control signal on its gate, and coupled between an input and product line. Additionally, the integrated circuit may further include a logical AND array and a logical OR array.
U.S. Pat. No. 6,711,069 to Lienau and entitled Register having a ferromagnetic memory cells describes a register. There is described use of a non-volatile ferromagnetic memory cell to store binary data in a register or flip-flop circuit. There is described a latching circuit, comprising an input line entering the latching circuit for receiving a signal, an output line, electrically coupled to the input line, for outputting the signal, and a ferromagnetic bit and sensor coupled between the input line and the output line, to store a form of the signal in the ferromagnetic bit even when power has been suspended to the latching circuit.
U.S. Pat. No. 6,545,908 to Lienau and entitled Dual conductor inductive sensor for a non-volatile random access ferromagnetic memory describes a nonvolatile ferromagnetic RAM device which is capable of reading the data stored in each magnet quickly and efficiently utilizing a minimal number of components. Specifically there is a nonvolatile ferromagnetic RAM which is capable of reading the data stored in each magnetic bit. The ferromagnetic memory cell, comprising of a base that is oriented in a horizontal plane. There is also a bit, made of a ferromagnetic material, having: a height that is oriented perpendicular to the horizontal plane of the base, and a polarity that can be directed along the height. Additionally, there is a sense line, positioned proximate the bit sufficient to detect the directed polarity of the bit; and a write line, positioned proximate the bit sufficient to direct the polarity of the bit. Additionally, there is a detector, coupled to the sense line; and a sample drive line, positioned proximate the bit to transmit an electric pulse that will increase the directed polarity of the bit sufficient to induce a wave into the sense line that can be detected by the detector.
U.S. Pat. No. 6,341,080 to Lienau and entitled Hall effect ferromagnetic random access memory device and its method of manufacture describes a Hall effect ferromagnetic non-volatile random access memory cell comprising a Hall effect sensor adjacent to a ferromagnetic bit which is surrounded by a drive coil. The coil is electrically connected to a drive circuit, and when provided with an appropriate current creates a residual magnetic field in the ferromagnetic bit, the polarity of which determines the memory status of the cell. The Hall effect sensor is electrically connected via four conductors to a voltage source, ground, and two read sense comparator lines for comparing the voltage output to determine the memory status of the cell. The read and write circuits are arranged in a matrix of bit columns and byte rows. A method for manufacturing said Hall effect ferromagnetic non-volatile random access memory cell.
U.S. Pat. No. 6,330,183 to Lienau and entitled Dual conductor inductive sensor for a non-volatile random access ferromagnetic memory describes a nonvolatile ferromagnetic RAM device which is capable of reading the data stored in each magnet quickly and efficiently utilizing a minimal number of components. Specifically there is a nonvolatile ferromagnetic RAM which is capable of reading the data stored in each magnetic bit. The ferromagnetic memory cell, comprising of a base that is oriented in a horizontal plane. There is also a bit, made of a ferromagnetic material, having: a height that is oriented perpendicular to the horizontal plane of the base, and a polarity that can be directed along the height. Additionally, there is a sense line, positioned proximate the bit sufficient to detect the directed polarity of the bit; and a write line, positioned proximate the bit sufficient to direct the polarity of the bit. Additionally, there is a detector, coupled to the sense line; and a sample drive line, positioned proximate the bit to transmit an electric pulse that will increase the directed polarity of the bit sufficient to induce a wave into the sense line that can be detected by the detector.
U.S. Pat. No. 6,317,354 to Lienau and entitled Non-volatile random access ferromagnetic memory with single collector sensor describes a non-volatile RAM device is disclosed which utilizes a plurality of ferromagnetic bits each surrounded by a coil of a write line for directing the remnant polarity thereof is disclosed. The direction of magnetic remnance in each bit is dictated by the direction of a current induced into write line. Further, a magneto sensor comprising a magneto resistor coupled to a collector is placed approximate each bit. The magneto resistor is coupled to a control circuit for receiving current. The current passing across magneto resistor is biased in a direction either right or left of the original current flow direction. The collector is coupled to a sense line, which in turn, is coupled to an amplifier. When current flow is biased in the direction of the collector, the serial resistance of the magneto resistor will be decreased, and the sense line will receive a high amount of current. However, when current flow is biased in the direction away from the collector, then the serial resistance of the magneto resistor will be effectively increased, and the sense line will receive a small amount of current. The presence and amount of current in the sense line is amplified and detected by the amplifier.
U.S. Pat. No. 6,288,929 to Lienau and entitled Magneto resistor sensor with differential collectors for a non-volatile random access ferromagnetic memory describes a non-volatile RAM device which utilizes a plurality of ferromagnetic bits each surrounded by a coil of a write line for directing the remnant polarity thereof is disclosed. The direction of magnetic remnance in each bit is dictated by the direction of a current induced into write line. Further, a magneto sensor comprising a magneto resistor coupled to a pair of collectors is placed approximate each bit. The magneto resistor is coupled to a control circuit for receiving current. The current passing across magneto resistor is biased in a direction either right or left of the original current flow direction. The collectors are coupled to a pair of sense lines, which are in turn, coupled to a voltage differential amplifier. The collector in the direction of biased current flow, will receive a greater number of electrons than the other collector, and therefore have a greater negative charge. This voltage differential is conducted through the sense lines to the voltage differential amplifier, where it is amplified and detected.
U.S. Pat. No. 6,266,267 to Lienau and entitled Single conductor inductive sensor for a non-volatile random access ferromagnetic memory describes a nonvolatile ferromagnetic RAM device and method that is capable of reading the data stored in each magnet quickly and efficiently utilizing a minimal number of components. Specifically, there is a nonvolatile ferromagnetic RAM which is capable of reading the data stored in each magnetic bit. There is a ferromagnetic memory cell, comprising a bit, made of a ferromagnetic material, having a remnant polarity. A write line, located proximate the bit, is coupled to receive: 1) a first current sufficient to create the remnant polarity, and 2) a pulsed second current, insufficient to create any remnant polarity, but sufficient to potentially fluctuate the remnant polarity during the second current pulse. A sense line, positioned proximate the bit, has the purpose of detecting any potentially created remnant polarity fluctuation.
U.S. Pat. No. 6,229,729 to Lienau and entitled Magneto resistor sensor with diode short for a non-volatile random access ferromagnetic memory describes a non-volatile RAM device is disclosed which utilizes a plurality of ferromagnetic bits each surrounded by a write coil for directing the remnant polarity thereof is disclosed. The direction of magnetic remnance in each bit is dictated by the direction of a current induced into write coil. Further, a magneto sensor comprising a magneto resistor coupled to a diode is placed approximate each bit. The magneto resistor is coupled to a sense line, and receives current at a first point of attachment, and returns current at a second point of attachment. The current passing across magneto resistor is biased in a direction either right or left of the original current flow direction. If current is biased toward the anode end of diode then it is complimentary to the preferred flow direction of diode, and flows easily there across. The ultimate effect is that the serial resistance of magneto resistor is reduced, allowing a greater amount of current to pass into the sense line. When current is biased toward the cathode end of diode, then it is contrary to the preferred flow direction of the diode, and does not flow easily there across. The ultimate effect is that the serial resistance of magneto resistor is increased, allowing a smaller amount of current to pass into sense line. The presence and amount of current found in the sense line between the bit and the detector determines whether a digital value of “1” or “0” is stored in the magnetic bit. A method for storing binary data is also disclosed.
U.S. Pat. No. 6,140,139 to Lienau and entitled Hall effect ferromagnetic random access memory device and its method of manufacture describes a Hall effect ferromagnetic non-volatile random access memory cell comprising a Hall effect sensor adjacent to a ferromagnetic bit which is surrounded by a drive coil. The coil is electrically connected to a drive circuit, and when provided with an appropriate current creates a residual magnetic field in the ferromagnetic bit, the polarity of which determines the memory status of the cell. The Hall effect sensor is electrically connected via four conductors to a voltage source, ground, and two read sense comparator lines for comparing the voltage output to determine the memory status of the cell. The read and write circuits are arranged in a matrix of bit columns and byte rows.
U.S. Pat. No. 5,295,097 to Lienau and entitled Nonvolatile random access memory describes a nonvolatile random access memory is disclosed having a substrate carrying separate magnetically polarizable domains each surrounded by a full write loop member and arranged to penetrate the Hall channel of a dual drain FET with its residual magnetic field. The domains are organized in word rows and bit columns, are each written to by a single full write current through the surrounding loop member and each read by a comparator connected to the FET drains.
One or more of the inventions heretofore known suffer from a number of disadvantages which include only having bits with binary states; having a low memory/volume ratio; requiring the inclusion of many components; requiring the inclusion of many manufacturing steps; requiring many masks to produce; consuming a great amount of power per bit; requiring exotic chemical processing; and being otherwise expensive and/or difficult to manufacture.
What is needed is a memory device and/or method that solves one or more of the problems described herein and/or one or more problems that may come to the attention of one skilled in the art upon becoming familiar with this specification.